BACKGROUND OF THE INVENTION
i) Field of the Invention:
[0001] The present invention relates to a discharge lamp to be used for a copy lighting
device for information apparatuses such as a facsimile, a copier, an image reader
and the like, a lightning bulletin board, a large display device, and the like, and
a method for producing the discharge lamp.
ii) Description of the Related Arts:
[0002] Conventionally, a fluorescent lamp is used as a light source for a copy lighting
device of information apparatuses such as a facsimile, a copier, an image reader and
the like. For such uses, a small type, a high luminance, a long life and high reliability
are required for the lamp. Since the conventional fluorescent lamp is provided with
electrodes such as filament electrodes within the tube, the structural limitation
imposed by the electrodes is large, and a variety of attempts have been tried for
settling problems.
[0003] In Figs. 23a and 23b, for example, there is shown a conventional fluorescent lamp
disclosed in proceedings of 1991 annual conference of the Illumination Engineering
Institute of Japan. As shown in Figs. 23a and 23b , the fluorescent lamp 1 comprises
a cylindrical glass bulb 2 enclosing rare gases mainly composed of xenon gas therein,
a fluorescent substance layer 3 formed on the internal surface of the glass bulb 2,
a light output part 4 for emitting the generated light in the glass bulb 2 to the
outside, a pair of external electrodes 5a and 5b mounted on the external surface of
the glass bulb 2 and extending in the longitudinal direction thereof, and a power
source 7 for supplying power between the external electrodes 5a and 5b through lead
wires 6a and 6b.
[0004] When a voltage is applied between the external electrodes 5a and 5b from the power
source 7, a current flows between them due to the electrostatic capacity therebetween
and brings about a discharge between them both. By this discharge, UV (ultraviolet)
rays are generated within the glass bulb 2, and the generated UV rays excite the fluorescent
substance layer 3 formed on the internal surface of the glass bulb 2 to irradiate
visible light outside through the light output part 4.
[0005] In this conventional fluorescent lamp, the aforementioned various defects due to
the presence of the electrodes such as the filament electrodes within the glass bulb
2 can be improved upon. However, the following problems are still present. That is,
as shown in Figs. 23a and 23b, the distance between the electrodes on the opposite
side to the light output part 4 is almost the same as the width of the light output
part 4, and thus the sufficient electrode area can not be taken. Hence, a sufficient
light output can not be obtained. Also, as the charged pressure of the rare gases
within the glass bulb 2 is increased, the discharge between the electrodes 5a and
5b becomes unstable, and thus a fringe flicker is caused between the electrodes 5a
and 5b. Further, since the distance between the electrodes 5a and 5b is wide, the
size of the fringe caused between the electrodes 5a and 5b is wide. That is, due to
this fringe, the luminance distribution in the longitudinal direction of the fluorescent
lamp is uneven. The uneven luminance distribution brings about a problem in a case
where the fluorescent lamp is used for the copy lighting of information apparatuses,
where a plurality of fluorescent lamps are arranged to constitute an image display
device, or the like.
[0006] US-A-5,013,966 already discloses a discharge lamp comprising a substantially straight
gas bulb having a discharge gas charged therein and an electrode provided at each
longitudinal end portion of the bulb on the outer surface thereof. A high frequency
voltage is applied across the electrodes of the discharge lamp.
SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to provide a discharge lamp in view of the
aforementioned problems of the prior art, which is capable of obtaining a large light
output and a stable discharge.
[0008] It is another object of the present invention to provide a discharge lamp capable
of selectively generating a discharge in a plurality of parts.
[0009] It is still another object of the present invention to provide a method for producing
a discharge lamp capable of obtaining a large light output and stable discharge and
selectively generating a discharge in a plurality of parts.
[0010] The object is solved for the discharge lamp by the features of independent claims
1 and 6 and for the method by the features of claims 13 and 14. Modifications of the
discharge lamp according to the invention are provided by the subclaims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The present invention will more fully appear from the following description of the
preferred embodiments with reference to the accompanying drawings, in which:
Figs. 1a and 1b are schematic perspective and cross sectional views of a first embodiment
of a discharge lamp according to the present invention;
Fig. 2 is a graphical representation showing the relationship between the filled pressure
of rare gases in a cylindrical glass bulb and lamp efficiency of the discharge lamp
according to the present invention;
Fig. 3 is a graphical representation showing the relationship between the current
density flowing between external electrodes and lamp efficiency of the discharge lamp
according to the present invention;
Fig. 4 is a graphical representation showing the relationship between the frequency
of a voltage applied to the external electrodes and luminance of the discharge lamp
according to the present invention;
Fig. 5 is a graphical representation showing the relationship between the distance
between the external electrodes and a discharge start voltage of the discharge lamp
according to the present invention;
Figs. 6a and 6b are cross sectional views of a second embodiment of a discharge lamp
according to the present invention having a plurality of external electrode pairs
arranged in the peripheral direction of a cylindrical glass bulb;
Fig. 7 is a schematic perspective view of a third embodiment of a discharge lamp according
to the present invention having external electrodes arranged in the longitudinal direction
of a cylindrical glass bulb;
Fig. 8 is a schematic perspective view of a fourth embodiment of a discharge lamp
according to the present invention having a plurality of external electrode pairs
arranged in the longitudinal direction of a cylindrical glass bulb;
Figs. 9a and 9b are schematic perspective view of a fifth embodiment of a discharge
lamp according to the present invention having a light output part at one end of a
cylindrical glass bulb;
Figs. 10a and 10b are cross sectional and elevational views of a sicth embodiment
of a discharge lamp according to the present invention having a box form;
Fig. 11 is a cross sectional view of a seventh embodiment of a discharge lamp according
to the present invention including a glas bulb having a triangular cross section;
Fig. 12 is a cross sectional view of an eighth embodiment of a discharge lamp according
to the present invention including a glass bulb having an elliptical cross section;
Fig. 13 is a fragmentary cross sectional view showing the thickness of the glass bulb
having the elliptical cross section shown in Fig. 12;
Figs. 14a and 14b are perspective view of a ninth embodiment of a discharge lamp according
to the present invention having a plurality of external electrode pairs, in which
voltages or currents to be applied to the electrode pairs can be independently controlled;
Fig. 15 is a graphical representation showing the relationship between the position
from the center of the electrode pair and luminance of the discharge lamp shown in
Fig. 14a;
Figs. 16a and 16b are schematic perspective and cross sectional views of a tenth embodiment
of a discharge lamp according to the present invention having a plurality of external
electrode pairs, in which voltages or currents to be applied to the electrode pairs
can be independently controlled;
Figs. 17a and 17b are cross sectional and elevational views of an eleventh embodiment
of a box type discharge lamp according to the present invention to be used as one
pixel for a color image display device, including three primary color (R, G and B)
parts;
Figs. 18a and 18b and Figs. 19a and 19b are schematic perspective and cross sectional
views of twelfth and thirteenth embodiments of a discharge lamp according to the present
invention having a cylindrical glass bulb with hollowed section parts on the surface
between external electrode pairs;
Fig. 20 is an elevational view showing a method for producing a discharge lamp having
a cylindrical glass bulb with hollowed sections on the surface between external electrode
pairs according to the present invention;
Fig. 21 is an elevational view showing another method for producing a discharge lamp
having a cylindrical glass bulb with hollowed sections on the surface between external
electrode pairs according to the present invention;
Fig. 22 is a cross sectional view of a fourteenth embodiment of a discharge lamp according
to the present invention having electrodes formed on the internal surface of a container,
the inside of the electrode being covered by a dielectric layer; and
Figs. 23a and 23b are a partially cut away and a cross sectional view respectively,
of a conventional fluorescent lamp.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] Referring now to the drawings, wherein like reference characters designate like or
corresponding parts throughout the views and thus the repeated description thereof
can be omitted for brevity, there is shown in Fig. 1 the first embodiment of a discharge
lamp according to the present invention.
[0013] As shown in Fig. 1, in a fluorescent lamp 1 a glass bulb 2 has a straight cylinder
form having dimensions of, for example, a diameter of 10 mm and a length of 220 mm,
and a fluorescent substance layer 3 is formed on almost the entire internal surface
of the glass bulb 2. A rare gas such as xenon at a pressure such as 931 Pa (70 Torr)
is enclosed in the glass bulb 2. A part having a width such as approximately 4 mm
along the entire length of the glass bulb 2, on which the fluorescent substance layer
3 is not formed, constitutes a light output part 4 for emitting the light generated
within the glass bulb 2 to the outside. A pair of external electrodes 5a and 5b having
a width such as approximately 12 mm are mounted on the external peripheral surface
of the glass bulb 2 along the entire length thereof except at the light output part
4 spaced apart by, for example, approximately 2 mm less than the width of the light
output part 4 on the opposite side to the light output part 4. An insulating member
8 for preventing a dielectric breakdown between the electrodes 5a and 5b on the external
peripheral surface of the lamp is formed on the external surface of the glass in the
space between the external electrodes 5a and 5b. A power source 7 for supplying electric
power is connected to the external electrodes 5a and 5b through lead wires 6a and
6b.
[0014] Next, the operation of the fluorescent lamp having the above-described structure
will be described. That is, when a voltage is applied between the external electrodes
5a and 5b from the power source 7, the voltage is supplied to the xenon gas within
the glass bulb 2 through the glass of the dielectric substance to cause the discharge
between the electrodes 5a and 5b. At this time, the UV rays generated within the glass
bulb 2 excite the fluorescent substance layer 3 and are converted into visible light
at the fluorescent substance layer 3, and the generated visible light from the fluorescent
substance layer 3 is irradiated to the outside through the light output part 4.
[0015] The principle of the aforementioned light emission will now be described in detail.
That is, in the fluorescent lamp 1, since the discharge is taking place between the
electrodes 5a and 5b through the glass as the dielectric substance, the current flowing
through the glass bulb 2 is limited and the discharge is not developed from the glow
discharge to the arc discharge. Further, the discharge is not concentrated at a particular
place, and the discharge is caused from the entire internal surface of the glass bulb
2 facing the external electrodes 5a and 5b. If the thickness and the like of the glass
are constant and the dielectric property is substance is uniform, the current density
of the internal surface of the glass bulb 2 facing the electrodes 5a and 5b becomes
uniform and thus the density of the generated UV rays becomes almost uniform. Hence,
the generation of the visible light is also almost uniform. As a result, the luminance
distribution of the lamp surface becomes almost uniform. Further, the current flows
only directly after the polarity of the applied voltage is inverted, and the electric
charge is accumulated on the internal surface of the glass bulb 2 except that current
which flow to stop the current. As a result, the pulsed current flows in the lamp.
[0016] In addition, when the discharge state within the lamp is carefully observed, the
entire internal surface of the glass bulb 2 directed towards the external electrodes
5a and 5b is covered by the almost uniform light, and further many fine filiform discharges
between the opposite electrodes 5a and 5b are generated at almost the same interval
in a fringy form. When the rare gas is enclosed within the glass bulb 2, by this discharge,
first, the rare gas atom collides with an electron to be excited to a resonance level.
Since the pressure of the rare gas is high in the glass bulb 2, the excited atom having
this resonance level collides with another rare gas atom having a ground level to
form an excimer of a diatomic molecule. This excimer irradiates the UV rays to return
to two rare gas atoms having the ground level. Since the UV rays generated by the
excimer do not cause a self absorption like the resonant UV rays of the atom, almost
all of the UV rays reach the internal surface of the glass bulb 2 and are converted
into the visible light by the fluorescent substance layer 3 formed on the internal
surface of the glass bulb 2. Namely, in the light generation by the excimer, the brighter
light can be obtained. Further, when xenon is used as the rare gas, in comparison
with a glow discharge lamp having electrodes therein with much resonant UV rays of
xenon of 147 nm, there are mainly UV rays irradiated by the excimer of approximately
170 nm in the present fluorescent lamp. The long wavelength of the UV rays is advantageous
with regard to light generation efficiency and deterioration of the fluorescent substance.
[0017] In this embodiment, since the fluorescent lamp 1 has a length of 220 mm and the electrodes
5a and 5b are mounted on the external surface of the glass bulb 2 along the entire
length thereof, the discharge condition is almost constant along the entire length
of the glass bulb 2, and the entire length of the fluorescent lamp 1 becomes the effective
light generation part. For example, when the fluorescent lamp 1 is used for reading
a copy of A4 size, it is sufficient to use a lamp having almost the same length as
the width of the copy, and thus a further miniaturization of information apparatuses
is possible.
[0018] Further, since there are no electrodes within the fluorescent lamp 1, a limited life
due to consumption of the internal electrodes does not result, and there is no occurrence
total unusability due to a sudden breakdown of the lamp, which has been a serious
problem in the information apparatuses.
[0019] For example, by using a glass bulb of soda glass having a thickness of 0.6 mm and
M
2SiO
5: Tb (M=Y, Sc) as the fluorescent substance, when a voltage of 800 V at a frequency
of 50 kHz is applied between the external electrodes 5a and 5b, the luminance of approximately
30000 cd/m
2 on the light output part 4 is obtained. This voltage condition is the same easily
managable level as a usual cold cathode fluorescent lamp using mercury (Hg). Further,
its luminance is extremely high compared with that of a cold cathode lamp using a
glow discharge of xenon. Furthermore, since the glass bulb of the lamp of this embodiment
has a cylindrical form which is strong for use with a vacuum, the thickness of the
glass of the bulb 2 can be reduced, and thus the impedance of the glass as the dielectric
substance can be reduced. As a result, the lamp can be discharged at a low frequency
and a low voltage.
[0020] In Fig. 2, there is shown the relationship between an enclosed rare gas pressure
within a cylindrical glass bulb 2 and lamp efficiency of the fluorescent lamp 1 according
to the present invention. The lamp efficiency can be obtained from a value calculated
by dividing the luminance by the electric power. It is readily understood from Fig.
2 that, as the enclosed gas pressure is decreased, the lamp to be due to the fact
efficiency is suddenly reduced. This is considered that, since the light generation
is due to the UV rays generated by the excimer and the generation of the excimer is
due to the collision between the rare gas atoms, a low enclosed rare gas pressure
brings about a low probability of the excimer formation. The fine filiform discharge
can be observed at a pressure of more than 399 Pa (30 Torr). At a lower pressure than
30 Torr, the discharge is extended like a glow discharge, and the radiation of near
IR (infrared) rays of the atomic spectrum of the rare gas becomes strong. From the
viewpoint of the effective generation of the excimer and the use of its light generation,
the enclosed gas pressure is preferably more than 399 Pa (30 Torr).
[0021] In Fig. 3, there is shown the relationship between density of a current flowing between
the external electrodes 5a and 5b and the lamp efficiency of the fluorescent lamp
1 according to the present invention. In the fluorescent lamp of this embodiment,
since the discharge is generated at only the portions facing the external electrodes
5a and 5b, the characteristics of the lamp can be largely affected by the current
density rather than the whole amount of current flowing in the lamp. That is, since
the electrode area is large, the large electric power can be committed to the medium
for the discharge even at the low current density and hence the efficiency is high.
Further, when the current density is low, the intensity of the near IR in infrared
rays irradiated by the xenon atom is weak. In the lamp including the electrodes therein,
since the current density near the electrodes is high, the near IR rays as the atomic
spectrum of the rare gas are strong, which is detrimental to the copy reading in the
facsimile. Hence, it is necessary to use a filter for cutting the near IR rays. In
the fluorescent lamp of this embodiment, no such filter is required and it is quite
suitable for copy reading in the facsimile or the like.
[0022] In Fig. 4, there is shown the relationship between the frequency of the voltage applied
to the external electrodes 5a and 5b and the luminance of the fluorescent lamp 1 according
to the present invention. It is readily understood from Fig. 4 that the higher the
frequency, the higher the luminance obtained. The reason for this is as follows. That
is, since the voltage is applied from the external surface of the glass, as the frequency
is lowered, the impedance of the glass increases, and it is difficult to supply sufficient
electric power to the rare gas. Further, when the frequency is low, the discharge
is apt to be unstable, and uneven luminance is liable to be caused. Also, since the
noise is inclined to be caused when a relatively high voltage is used, the harsh noise
is apt to be generated in the audio frequency band. From the view points described
above, in this embodiment, the lamp is preferably supplied with a voltage a frequency
of more than 20 kHz. On the other hand, since, as the frequency is increased, the
larger electric power can be supplied and the luminance becomes higher, the current
density is increased and thus the efficiency drops. Further, by providing the electrodes
outside of the bulb, it is hard to avoid the generation of a magnetic noise, and in
order to avoid interference to a radio receiver or the like, the frequency of the
voltage is preferably less than 500 kHz lower than the radio frequency.
[0023] In Fig. 5, there is shown a discharge start voltage when an interval between the
external electrodes 5a and 5b is varied at an enclosed gas pressure of 399 Pa (30
Torr) in the fluorescent lamp 1 according to the present invention. It is apparent
from Fig. 5 that the discharge start voltage is increased almost in proportion to
the interval between the electrodes 5a and 5b. That is, it is considered that the
discharge system of this fluorescent lamp meets Paschen's law, that is, as the enclosed
gas pressure is increased, the discharge start voltage is raised. Hence, the interval
between the electrodes is preferably as narrow as possible, but, in practice, it is
preferably less than 3 mm. In the lamp of this embodiment, even when the interval
between the electrodes is narrow, the efficiency is not reduced, and as a result,
the discharge start voltage can be reduced, unlike a conventional fluorescent lamp
using a light generation of a positive column generated at a separate position from
the electrodes.
[0024] Further, since the UV rays are mainly generated on the internal surface of the lamp
facing the electrodes, when the electrode area is large, the light output is large.
In particular, when the opening angle of the light output part 4 is large and the
external electrodes 5a and 5b are positioned on the opposite side to the light output
part 4, it is very much effective to obtain the large light output.
[0025] Furthermore, since the discharge is stable, attributable to the narrow distance between
the electrodes 5a and 5b, the uniform luminance distribution can be obtained in the
axial or longitudinal direction of the cylindrical container such as the glass bulb
2. In addition, since, as the electrode interval is narrowed, the interval of the
fringy discharge is narrowed, by observing the discharge state, it is found that the
luminance distribution is further made uniform.
[0026] In Figs. 6a and 6b, there is shown the second embodiment of the discharge lamp according
to the present invention. Although there is provided one pair of external electrodes
in the first embodiment shown in Figs. 1a and 1b, in this embodiment, at least two
pairs of external electrodes 5a and 5b are formed on the external surface of the glass
bulb 2 in the peripheral direction thereof, as shown in Fig. 6a, or two electrodes
5a are formed on both sides of the electrode 5b in the peripheral direction of the
glass bulb 2, as shown in Fig. 6b. In this case, the discharge is caused between each
pair of electrodes and the operation is performed in the same manner with the same
effects as described above in the first embodiment.
[0027] In Fig. 7, there is shown the third embodiment of the discharge lamp according to
the present invention. In this embodiment, surface electrodes 5a and 5b are formed
on the external surface of the cylindrical glass bulb 2 so as to surround the peripheral
surface of the adjacent two halves obtained by dividing the glass bulb 2 in the longitudinal
direction. In this construction, the discharge is uniformly generated on the surface
of the electrode parts, and the same effects as those of the preceding present embodiments
can be obtained. In this instance, an insulating member (not shown) is preferably
provided in a gap between the electrodes 5a and 5b in order to prevent the dielectric
breakdown between the electrodes 5a and 5b on the external peripheral surface of the
lamp.
[0028] In the first to third embodiments, as described above, although the external electrodes
5a and 5b are formed over the entire external surface of the glass bulb 2 except the
light output part 4, when not so large a light output is required, the electrodes
5a and 5b can be formed on only part of the external surface of the glass bulb 2.
[0029] In Fig. 8, there is shown the fourth embodiment of the discharge lamp according to
the present invention. In this embodiment, a plurality of electrode pairs are arranged
on the external surface of the glass bulb 2 in the longitudinal direction thereof.
In this case, even in a long lamp, the UV rays generation amount becomes uniform at
any part in the longitudinal direction, and an improved luminance distribution over
the entire length of the lamp can be obtained. In the fluorescent lamp 1 shown in
Figs. 1a and 1b or Figs. 6a and 6b, of course, a plurality of electrode pairs can
be arranged in the longitudinal direction of the glass bulb 2 in the same manner as
described above.
[0030] In Figs. 9a and 9b, there is shown the fifth embodiment of the discharge lamp according
to the present invention. In this embodiment, one end of the cylindrical glass bulb
2 is formed to be transparent and a light output part 4 is formed in this transparent
end. A fluorescent substance layer 3 is formed on the internal surface of the cylindrical
glass bulb 2 except at the light output part 4 of the transparent end, and a pair
of external electrodes 5a and 5b are formed on substantially the entire external peripheral
surface of the cylindrical glass bulb 2 in the same manner as the first and third
embodiments shown in Fig. 1a and Fig. 7. This structure is suitable for applications
requiring an extremely large light output. In order to obtain the large light output,
it is necessary to supply a larger electric power, and in turn, as shown in Fig. 3,
in order to obtain a high efficiency, it is required to restrict the current density
to a low value. In order to supply the large electric power while the current density
is kept at a the low value, it is sufficient to enlarge the electrode area.
[0031] In the fluorescent lamp of this embodiment, since the peripheral surface area can
be enlarged even when the area of the end part as the light output part 4 of the cylindrical
glass bulb 2 is small, the electrode area can be enlarged. That is, while the current
density is maintained at a low value, the large electric power can be supplied to
obtain the fluorescent lamp having a high efficiency and a large light output. Further,
since there is no light interception member such as electrodes within the glass bulb
2, the light is not lost. The fluorescent substance layer 3 is further formed on the
end part opposite to the light output part end part of the glass bulb 2, and this
fluorescent substance not only converts the UV rays into the visible light but also
functions to reflect the light generated within the glass bulb 2. As a result, an
extremely bright light can be output to the outside through the light output part
4. Hence, the fluorescent lamp can be properly used for pixels of a display device
or the like required to display an image outdoors in the daytime.
[0032] Further, the electrodes can be formed on the end part opposite to the light output
part in addition to the peripheral surface of the glass bulb 2, and in this case,
the whole electrode area can be further enlarged. Thus, a further large electric power
can be supplied. Further, the UV rays are generated on mainly the surfaces of the
electrodes, and the bright lighting effect of the electrode surfaces is further added
to obtain the fluorescent lamp having further high efficiency and brightness.
[0033] In this embodiment, the two opposite end parts of the glass bulb 2 can be either
a flat surface or a curved surface. Further, the end part opposite to the light output
part 4 is not restricted to the fluorescent substance layer and can be formed into
a structure reflecting the light such as various reflecting films, a white color substance
or the like.
[0034] In Figs. 10a and 10b, there is shown the sixth embodiment of the discharge lamp according
to the present invention. In this embodiment, a box type container for enclosing the
medium such as the rare gas for the discharge is used in place of the cylindrical
glass bulb used in the first to fifth embodiments. Of course, the size and shape of
the container for the discharge medium enclosure is not restricted and any shape such
as a straight cylinder, a sphere, a triangular column, a box, or the like can be used.
In this embodiment, a pair of flat electrodes 5a and 5b are mounted on the entire
external surface of the bottom of the box container, and a fluorescent substance layer
3 is formed on the internal surface of the bottom. The top is a light output part
4 opposite to the electrodes 5a and 5b.
[0035] In this embodiment, an AC voltage is applied between the external electrodes 5a and
5b to cause the discharge therebetween, and the light generation is carried out in
the same manner as described above to irradiate the light to the outside through the
light output part 4. In this case, the excimer is generated on the surface part of
the electrodes in the same manner as described above, and the uniform luminance distribution
can be performed to obtain the fluorescent lamp having high efficiency without unevenness
unlike a conventional fluorescent lamp using a light generation of a positive column
generated at a separate position from the electrodes.
[0036] In Fig. 11, there is shown the seventh embodiment of the discharge lamp according
to the present invention. In this embodiment, a triangular column glass bulb is used.
with regard to the triangular cross section of the glass bulb, the three vertex parts
are rounded and the three sides can be composed of a curved line having a larger radius
of curvature than a radius of curvature of the vertex parts. In this case, the external
electrodes 5a and 5b are formed on two side surfaces of the glass bulb and the light
output part 4 is formed on the other side surface. In this instance, the area of the
external electrodes 5a and 5b compared with the projection area of the light output
part 4 can be enlarged rather than the circular cross section of the cylindrical glass
bulb, and a brighter fluorescent lamp can be constructed.
[0037] In Fig. 12, there is shown the eighth embodiment of the discharge lamp according
to the present invention. In this embodiment, an elliptical column glass bulb having
an elliptical cross section is used, and the same effects and advantages as those
of the above-described embodiments can be obtained.
[0038] In this case, when the thickness of the glass bulb 2 is formed to be uniform, the
stress distribution of the glass bulb 2 becomes uneven. Hence, the thickness of the
small stress portions can be made relatively thin, as shown in Fig. 13 wherein t2
< t1. When the voltage is applied between the electrodes, the electrical field in
the discharge space is caused as the electrode - the dielectric substance layer (glass)
- the discharge space - the dielectric substance layer (glass) - the electrode. Since
the field intensity is in inverse proportion to the electrode distance, when the thinned
portions of the glass are partially formed, the dielectric substance (glass) layer
is thinned, and the field intensity of the thinned part is enlarged even when the
applied voltage is constant. As a result, the discharge start voltage can be lowered.
In this instance, as described above, when the discharge start voltage can be lowered,
a high voltage circuit conventionally provided for applying a high voltage at the
discharge start time can be omitted, and thus the present apparatus can be formed
by using only a voltage circuit for supplying a voltage at a usual discharge time.
[0039] In Figs. 14a and 14b, there is shown the ninth embodiment of the discharge lamp according
to the present invention. In this embodiment, a plurality of external electrode pairs
are arranged in the longitudinal direction of the cylindrical glass bulb 2, and an
electric power source 7 for applying a voltage or current and a switching element
connected in series with the electric power source 7 are provided for each electrode
pair so as to independently control the voltages or currents applied to the electrode
pairs. By carrying out an ON - OFF control of each switching element, only electrode
parts with a voltage applied start to perform the discharge to emit the light. This
utilizes the phenomenon that the discharge is generated at only the electrode parts
with a voltage applied and is not extended outside therefrom.
[0040] For instance, in the fluorescent lamp 1 shown in Fig. 14a, with the cylindrical glass
bulb 2 diameter of 10 mm and a light output part 4 opening angle of 180 0+, the fluorescent
substance layer 3 is formed on the half of the peripheral surface of the glass bulb
2, and a plurality of electrode pairs, each being composed of two electrodes having
a width of approximately 12 mm and arranged a distance of approximately 1 mm apart,
are arranged at a pitch of 36 mm. Now, when the voltage is applied to only one electrode
pair to cause it to discharge, the luminance distribution measured in the longitudinal
direction of the lamp is as shown in Fig. 15 wherein the center of the electrode pair
is determined to beat 0 mm on the positional scale.
[0041] In this case, when the discharge is generated between the electrode pair, the surfaces
of the electrode parts are brightly illuminated, and at the 0 mm position having no
electrode, the luminance is somewhat reduced. As described above, only the electrode
parts with the voltage applied can be illuminated, and a considerably high luminance
ratio of the illuminated part with reference to the adjacent unilluminated part can
be obtained. That is, in the system of this embodiment, the light generation of parts
of the glass bulb 2 can be controlled without providing a plurality of electrodes
within the glass bulb 2. Accordingly, the fabrication of this lamp can be extremely
easily carried out, and the influence of the unevenness of the electrode characteristics
is small compared with a light generation control of the conventional lamp including
a plurality of electrodes within the lamp. Hence, the reliability of the fluorescent
lamp according to the present invention is extremely high.
[0042] In Figs. 16a and 16b, there is shown the tenth embodiment of the discharge lamp according
to the present invention. In this embodiment, a plurality of external electrode pairs
are formed on approximately half the external peripheral surface of the cylindrical
glass bulb 2 and are arranged in the longitudinal direction of the glass bulb 2, and
the fluorescent substance layer 3 is formed on approximately half the internal peripheral
surface facing the electrodes. The plurality of electrode pairs are connected to one
electric power source 7 through the respective switching elements. In the fluorescent
lamp having the above-described construction, the projection area of the light output
part 4 can be made maximum. This means that the rate of the lighting area against
the image display area can be made large when this fluorescent lamp is applied to
an image display device hereinafter described in detail, and a high quality display
device can be obtained.
[0043] In Figs. 17a and 17b, there is shown the eleventh embodiment of a box type fluorescent
lamp 30 according to the present invention to be used as one pixel for a color image
display device. In this embodiment, the fluorescent lamp 30 includes three primary
color illumination parts 31,32 and 33 of red R, green G and blue B. A plurality of
fluorescent lamps 30 as the pixels are arranged in a matrix form on a flat surface
to constitute a color image display device.
[0044] In the fluorescent lamp shown in Figs. 14a and 14b or Figs. 16a and 16b, the discharge
is generated between each electrode pair, but the generated light is projected to
the outside. When these fluorescent lamps are used for a display device, the outline
of the pixel becomes dim. Further, the discharge can be generated between the adjacent
electrode pairs. In order to improve these problems, other embodiments of the fluorescent
lamps are developed as shown in Figs. 18a and 18b and Figs.19a and 19b.
[0045] In Figs. 18a and 18b, there is shown the twelfth embodiment of a fluorescent lamp
1 according to the present invention. In this embodiment, hollow portions 2a are formed
on the peripheral surface of the cylindrical glass bulb 2 between the electrodes constituting
the electrode pairs of the fluorescent lamp shown in Fig. 14b. In this case, by providing
the hollow portions 2a on the glass bulb 2 between the electrode pairs, the mixing
of the light generated at the adjacent electrode pairs can be largely reduced. By
using this fluorescent lamp in the display device, an image display device having
a simple construction can be produced, and a clear outline display can be performed.
[0046] In Figs. 19a and 19b, there is shown the thirteenth embodiment of a fluorescent lamp
1 according to the present invention. In this embodiment, hollow portions 2a are formed
on the peripheral surface of the cylindrical glass bulb 2 between the electrodes constituting
the electrode pairs of the fluorescent lamp shown in Fig. 16a. The same effects as
those of the twelfth embodiment shown in Figs. 18 a and 18b can be obtained.
[0047] In Fig. 20, there is shown one method for producing a discharge lamp having the hollow
portions 2a on the peripheral surface of the cylindrical glass bulb 2 between the
external electrode pairs according to the present invention. In this embodiment, before
one open end of the glass bulb 2 is closed, the glass bulb 2 is heated at the positions
where the hollow portions 2a by are to be formed a heating device 40. During the heating
of the glass bulb 2, the gas enclosed in the glass bulb 2 is sucked from the open
end of the glass bulb 2, by using an exhaust system (not shown) such as a vacuum pump,
to reduce the pressure in the glass bulb 2. Then, the portions which have become softened
by the heating become depressed by virtue of the reduced pressure in the glass bulb
2 to thus form the hollow portions 2a on the glass bulb 2 of the fluorescent lamp
shown in Figs. 18a and 18b or Figs. 19a and 19b.
[0048] In Fig. 21 there is shown another method for producing a discharge lamp having the
hollow parts 2a on the peripheral surface of the cylindrical glass bulb 2 between
the external electrode pairs according to the present invention. In this embodiment,
the inside of the glass bulb 2 is sucked to reduce the pressure inside thereof in
advance, and, after the discharge medium such as the rare gas is enclosed in the reduced
glass bulb 2 so that the pressure in the glass bulb 2 is still lower than the atmospheric
pressure, the glass bulb 2 is heated at positions where the hollow portions 2a are
to be fomed by the heating device 40. During the heating of the glass bulb 2, the
portions which have become softened by the heating become hollow due to the difference
between the inside pressure of the glass bulb 2 and the atmospheric pressure to thus
form the hollow portions 2a on the glass bulb 2 of the fluorescent lamp shown in Figs.
18a and 18b or Figs. 19a and 19b.
[0049] In the above-described embodiments according to the present invention, although the
surface electrodes are formed by the sheet form electrodes, net form electrodes or
electrodes formed by arranging a plurality of linear materials in parallel can also
be used. Further, although a plurality of electrodes are arranged in the axial direction
or perpendicular direction of the cylindrical container or the like, the electrodes
can be arranged in an inclined direction of the container. Also, although the electrodes
are mounted on the external surface of the glass bulb 2 and the discharge is generated
between the electrodes via the glass of the dielectric substance, the electrodes can
be embedded in the dielectric substance.
[0050] In Fig. 22, there is shown the fourteenth embodiment of a fluorescent lamp according
to the present invention having electrodes formed on the internal surface of a box
type container, the inside of the electrodes being covered by a dielectric layer.
In this embodiment, the electrodes 5a and 5b are formed on the internal surface of
a container body 9, and then the dielectric substance is formed on the internal surface
side of the electrodes so as to cover the same by a vapor deposition or the like to
form a dielectric substance layer 50. A fluorescent substance layer 3 is formed on
the dielectric substance layer 50 opposite to a light output part 4. The light output
part 4 is formed of a glass material, but the material of the container body 9 is
not restricted to glass material. In this embodiment, the container body 9 is formed
of a ceramic material. In this instance, the dielectric substance layer 50 is not
subjected to a stress caused by the pressure difference between the inside and the
outside of the fluorescent lamp, and thus it can be made thinner compared with the
above-described embodiments. As a result, the field intensity of the discharge space
can be enlarged, and the impedance of the dielectric substance layer 50 can be reduced.
Hence, the discharge of the fluorescent lamp can be carried out at a low voltage.
[0051] In the aforementioned embodiments according to the present invention, although xenon
is used as the rare gas enclosed within the lamp, another rare gas such as krypton,
argon, neon or helium, a mixture of at least two rare gases or another medium for
discharging can be used.
[0052] Further, although the present invention is applied to the fluorescent lamp, the UV
rays generated by the discharge are not necessarily converted into visible light and
can be utilized as a UV lamp.
[0053] As described above, according to the present invention, the following effects can
be obtained.
(1) Since the area of the surface electrodes can be widened compared with the conventional
lamp, a large light output can be obtained.
(2) Since the edges of the surface electrodes are made close to one another, the discharge
becomes stable.
(3) Since the discharge is generated at only the electrode parts to which the voltage
is applied, a plurality of electrode pairs are mounted on one fluorescent lamp, and
by selectively applying the voltage to the electrode pairs, a plurality of parts divided
in one fluorescent lamp can be selectively illuminated. Hence, when this fluorescent
lamp is used for illumination, the number of the electrode pairs that the voltage
is applied to is varied to change the luminance, illumination positions and the like.
(4) In the case of the fluorescent lamp in which a plurality of divided parts are
selectively illuminated, by providing hollow portions between the electrode pairs,
the discharge between the adjacent two electrode pairs can be prevented, and the leakage
of light from the electrode pair illuminating to the outside can also be prevented.
(5) By using the method for producing the fluorescent lamp having hollow portions,
the fluorescent lamp can be easily produced.
1. Discharge lamp (1), comprising:
a container (2) for enclosing a medium for discharge therein; and
at least one surface electrode pair (5a,5b) extending along the entire length of the
container (2) to which electrode pair (5a,5b) predetermined voltage is to be applied
to excite the discharge space within the container (2),
said surface electrode pair (5a,5b) having two ends, characterized in that a relative
distance between one pair of ends facing each other being shorter than a relative
distance between the other pair of ends facing each other.
2. Discharge lamp according to claim 1, characterized in that the relative distance between
said one pair of ends facing each other being shorter than the relative distance between
said other pair of ends facing each other is sufficient for ensuring electrical insulation
between said one pair of ends.
3. Discharge lamp according to claim 1 or 2, characterized in that the form of the container
(2) is a cylinder, and at least one beltlike electrode pair (5a,5b) is mounted on
a peripheral surface of said cylindrical container (2) on opposite sides discharge
space.
4. Discharge lamp according to claim 1 or 2, characterized in that the form of said container
is a box, and at least one electrode pair (5a,5b) is mounted on one surface of the
box container.
5. Discharge lamp according to any of claims 1 to 4, characterized in that a plurality
of surface electrode pairs (5a,5b) are mounted on surfaces of said container (2),
and said predetermined voltage is selectively applied to said surface electrode pairs
(5a,5b).
6. Discharge lamp (1), comprising:
a cylindrical container (2) for enclosing a medium for discharge therein; and
at least one surface electrode pair (5a,5b) to which a predetermined voltage is to
be applied, mounted so as to wind around a pheriphery of said cylindrical container
(2).
said surface electrode pair (5a,5b) being arranged to be adjacent to each other in
a direction of an axis of said cylindrical container (2),
characterized in that a plurality of surface electrode pairs (5a,5b) are mounted
on surfaces of said container (2), and said predetermined voltage is selectively applied
to said surface electrode pairs (5a,5b).
7. Discharge lamp according to any claims 1 to 6, characterized in that a rare gas is
enclosed in the container (2), and an excimer of the rare gas is generated by the
discharge between said electrodes (5a,5b).
8. Discharge lamp according to claim 7, said rare gas is xenon.
9. Discharge lamp according to claim 3 or 6, characterized in that the cross section
of said cylindrical container (2) is a circle.
10. Discharge lamp according to claim 3 or 6, characterized in that the cross section
of said cylindrical container (2) is approximately a triangle.
11. Discharge lamp according to claim 3 or 6, characterized in that the cross section
of said cylindrical container (2) is an ellipse.
12. Discharge lamp according to claim 6, wherein said container (2) includes hollow portions
(2a) between said electrode pairs (5a,5b).
13. Method for producing the discharge lamp according to claim 12, characterized by the
steps of heating predetermined parts of said container (2), and reducing the pressure
within said container (2) so that said container (2) becomes hollow at the heated
parts.
14. Method for producing the discharge lamp accoding to claim 12, characterized by the
steps of sealing said container (2) at a predetermined pressure lower than an atmospheric
pressure, and heating predetermined parts of said container (2) so that said container
(2) becomes hollow at the heated parts.